HR: 1330h
AN: T42A-0274    [PDF]
TI: The role of interfaces in plastic flow of two-phase rocks
AU: Xiao, X
EM: xhxiao@mit.edu
AF: EAPS, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: Dresen, G
EM: dre@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegraphenberg D424, Potsdam, 14473 Germany
AU: * Evans, B
EM: brievans@MIT.EDU
AF: EAPS, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AB: In polyphase materials, strain hardening is often related to the stress transfer from a weak phase to a stronger phase across an interphase boundary. Thus, interphase bonding may be an important aspect of composite deformation. Previous analytical and experimental approaches demonstrate that perfect bonding between rigid inclusions and matrix increases the internal stress in the inclusions substantially. Various models have been used to calculate the stresses within the two phases. Eshelby, estimated the internal stress arising from the misfit between the inclusion and the infinite isotropic matrix, by introducing the concepts of constrained strain (e$^{C}$) and equivalent transformation strain (e$^{T}$). Further extensions applicable at finite volume fraction of inclusion show that this model is useful for predicting a wide range of composite properties. In this study, we used the Eshelby-Mori-Tanaka (EMT) model (e.g., Eshelby, 1957; Mori and Tanaka, 1973; Murali and Weng, 1993) to describe the plastic flow of two-phase aggregates. The components of internal stresses in the matrix and inclusion are calculated by the EMT model. Based on the end-member flow laws, strain rates in each phase and the mean strain rate of the two-phase aggregates can then be calculated for both creep and constant-rate process. Using experimental data from the literature, we calculated the aggregate strength of anhydrite-halite, plagioclase-clinopyroxene, calcite-halite, calcite-quartz and anorthite-quartz mixtures.The model appears to overestimate the stress concentrations in inclusions and the bulk strengths when the strength contrast between the component phases is relatively high (anorthite-quartz and calcite-quartz aggregates). The agreements can be improved by relaxing stresses arising from misfit strain (e.g. by invoking interface sliding). Anorthite-quartz aggregates show less strengthening when high concentration of water-related defects are present. If these defects are present at grain boundaries, and if they weaken the interfacial bonding, the EMT model would be consistent with the relatively small strengthening observed in experiments. The calcite-quartz aggregates show less strengthening at high pore pressure (or low effective pressure), perhaps because high pore pressure allows the interface to relax stress transferring from weaker calcite matrix to the stronger quartz particles.
DE: 3902 Creep and deformation
DE: 5120 Plasticity, diffusion, and creep
DE: 8020 Mechanics
DE: 8159 Rheology--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting